Washington University in St. Louis is offering volunteers $3,500 to only eat fast food from McDonald's, Burger King, Taco Bell, KFC and Pizza Hut for the next three months. The study is to help understand obesity and why only some overweight people develop diabetes and cardiovascular risk factors. The only stipulation to the study? Participants must gain 5 percent of their body weight over the three months.

Despite the inherent unhealthiness of their menu items, some fast food chains are trying to support those affected by diabetes. Last year, KFC donated portions from KFC mega jug sales to benefit diabetes research.